Arguments from Ontology Chapter 2 Arguments from Ontology “It can’t be human because it contradicts, ontologically” H aving established the metaphysical principles involved in the ever-changing life of Johnny, our discussion now turns to exactly when Johnny arrived on the scene. Some argue that the very metaphysical principles outlined in the previous chapter preclude the possibility that the embryo is Johnny. If correct, such “arguments from ontology” are extremely powerful and decisive. Johnny is clearly a substance, and just as clearly he changes. Explaining this requires the metaphysical principles outlined previously. If asserting that the embryo is Johnny contradicts these principles, then those same principles would require us to say that Johnny comes to be at some later time. In general, these sorts of arguments fall into three broad categories : arguments from priority, complementarity, and disposition. 46 Arguments from Ontology 47 Ontological Priority The most basic argument against the humanity of the embryo is simply a matter of logical priority. The argument in summary is that “human embryo” implies a metaphysical contradiction. As noted above, every substance (including a human being) has attributes or characteristics that are unique to it and that are caused by the substantial form. The argument from ontological priority begins from the premise that an embryo clearly lacks those uniquely human traits. To insist that, nevertheless , the embryo is a human because it is on the way to developing those unique traits is to make the embryo human before it is human—a contradiction. Everything that is a human has distinctly human traits. Nothing that is only developing distinctly human traits yet has them. Hence, nothing that is only developing distinctly human traits can be human now. The seeds of this objection can be found in a classic 1970 article by Joseph Donceel.1 Our knowledge of embryonic development has grown considerably in the intervening span of years, but this and other articles by Donceel still carry much force because of their fundamental (i.e., metaphysical) nature, and the argument remains quite influential. For example, in 1988, Norman Ford addressed Donceel’s arguments in his own influential book When Did I Begin?, Stephen Heaney discussed it at length in an article for The Thomist in 1992, and Jason Eberl took it up again in 2005.2 In his article, Donceel observes that in the early stages of development “there is not at once a highly organized body, a body with sense 1. Joseph F. Donceel, “Immediate Animation and Delayed Hominization,” Theological Studies 31 (1970): 76–105. 2. Norman M. Ford, When Did I Begin?: Conception of the Human Individual in History, Philosophy, and Science (Cambridge: Cambridge University Press, 1988); S. J. Heaney, “Aquinas and the Presence of the Human Rational Soul in the Early Embryo,” The Thomist, 56, no. 1 (1992): 19–48; Jason T. Eberl, “Aquinas’s Account of Human Embryogenesis and Recent Interpretations,” Journal of Medicine and Philosophy 30 (2005): 379–94. Other recent works borrowing from, responding to, or influenced by Donceel include Robert Pasnau, Thomas Aquinas on Human Nature (New York: Cambridge University Press, 2002); Pasnau, “Souls and the Beginning of Life: A Reply to Haldane and Lee,” Philosophy 78 (2003): 521–31; John Haldane and Patrick Lee, “Aquinas on Human Ensoulment, Abortion and the Value of Life,” Philosophy 78 (2003): 255–78; and Haldane and Lee, “Rational Souls and the Beginning of Life: A Reply to Robert Pasnau,” Philosophy 78 (2003): 532–40. 48 Arguments from Ontology organs and a brain,”3 and a body and a brain of a certain sort are definitely hallmarks of what we call human: “The human body is not a reality in and by itself. Its quantitative, visible features may be said to be rooted in it, to derive from it, only if the body is considered as animated by the soul.... All man’s positive features ... derive totally from the soul.”4 The absence of such characteristically human attributes implies the absence of what makes a thing be what it is, that is, substantial form (soul), which in turn implies the absence of the human person as a whole. As Donceel puts it, “whatever is growing in the mother’s womb is [only] potentially, virtually, a human body,”5 and what is only “potentially ” or “virtually” something is not actually that thing. While the embryo may be developing characteristically human traits, it doesn’t have them yet, and becoming is not the same as being. To claim otherwise (i.e., that the...

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